Light Emitting Diodes (LEDs) refer to a semiconductor diode that emits light via generation and recombination of carriers, i.e. electrons and holes, in P-N junctions of a compound semiconductor. The LED consumes less power and has several to several dozen times the lifespan of conventional light bulbs or fluorescent lights, thereby being highly advantageous in terms of power reduction and durability. Additionally, the LED can be placed in a narrow space and is resistant to vibration. LED-based light emitting devices are used as display devices and backlights, and research is under way to apply them to general lighting. In recent years, white LEDs have come out in the marketplace, adding to already-available monochromatic LEDs, such as red LEDs, blue LEDs, and green LEDs. White LED-based light emitting devices are expected to experience rapidly increased demand along with an increase in application of such light emitting devices to automobile products, lighting products, and the like.
Humans have a circadian rhythm in which the physiological process is repeated in a roughly-24-hour cycle. For example, cortisol and melatonin, known as the “stress hormone” and the “sleep hormone,” respectively, have a great influence on physical activity and sleeping, respectively. As a basis of daily physical activity, the level of cortisol undergoes diurnal variation with an increased level during the daytime and the lowest level occurring around midnight. On the other hand, the level of melatonin acting as hormone for midnight sleeping decreases during the daytime and increases at night, thereby promoting healthy levels of sleep while preventing drowsiness during the daytime.
Light generally affects such a physiological rhythm in humans, and sunlight in particular has a very great influence on humans. The color temperature of sunlight is higher than 6000 K before noon and gradually decreases afternoon. Color temperature is a physical value of color of a light source measured in degrees Kelvin (K). As the color temperature increases, the light source radiates blue light, and, as the color temperature decreases, the light source radiates strong red-yellow light. Additionally, a higher color temperatures facilitate increased brain activity and concentration, whereas a lower color temperature facilitates reasoning and relaxation.
As such, light provides various feelings and great influences on the physiological rhythms depending on the wavelengths and color temperature thereof, while causing various disorders, such as impaired digestion, chronic fatigue, and the like, in the case of failing to properly accommodate to variation of the light. Accordingly, various efforts have been made to develop lighting devices which can operate in consideration of the circadian rhythm of humans.
A conventional LED-based light emitting device employs various means for achieving white light emission. Generally, phosphors are disposed around an LED chip such that white light can be obtained by mixing some of primary emission light from the LED with secondary emission light having undergone wavelength conversion through the phosphors. Examples of phosphors for realizing white light emission include garnet phosphors, thiogallate, sulfide, silicate, oxynitride, and the like. However, when the light emitting devices employs such phosphors, there are disadvantages of a narrow range in color temperature, a very low color rendering index, and instability of a lamp. In other words, it is difficult to manufacture a light emitting device capable of providing various spectra or color temperatures. Furthermore, since red-based phosphors have a lower photo efficiency, it is necessary to increase power and the amount of phosphors in order to realize white light having a lower color temperature with a blue or ultraviolet-LED chip and the phosphors.
The present invention is conceived to solve the problems of the conventional techniques as described above, and it is an aspect of the present invention to provide a light emitting device that includes a plurality of light emitting parts in a single package to realize white light of various spectra and color temperatures.
It is another aspect of the present invention to provide a light emitting device, the spectrum and color temperature of which is capable of being adjusted depending upon the physiological rhythms of human.
It is a further aspect of the present invention to provide a light emitting device capable of realizing white light having a lower color temperature without significantly increasing power and phosphors.
In accordance with an aspect of the present invention, the above and other features of the present invention can be accomplished by the provision of a light emitting device capable of emitting light having various color temperatures. The light emitting device includes a first light emitting part, a second light emitting part, and a third light emitting part. The first light emitting part includes a first LED chip and a first phosphor, and emits a daylight color having a color temperature of 6000 K or more; the second light emitting part includes a second LED chip and a second phosphor, and emits white light having a color temperature less than 6000 K; and the third light emitting part includes a third LED chip which emits light in a visible range of 580 nm or more. The second and third light emitting parts are operable independently of the first light emitting part and realize a warm white color having a color temperature of 3000 K or less with the white light emitted from the second light emitting part and the light emitted from the third light emitting part.
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 1:a(MIO).b(MII2O).c(MIIX).dAl2O3e(MIIIO).f(MIV2O3).g(MVoOp).h(MVIxOy)  <Chemical Formula 1>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Au, and Ag; MIII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Mn; MIV is at least one selected from the group consisting of Sc, B, Ga, and In; Mv is at least one selected from the group consisting of Si, Ge, Ti, Zr, Mn, V, Nb, Ta, W, and Mo; MVI is at least one selected from the group consisting of Bi, Sn, Sb, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; X is at least one selected from the group consisting of F, Cl, Br, and I; and a, b, c, d, e, f, g, o, p, h, x, and y are respectively set in the ranges of: 0<a≦2, 0≦b≦2, 0≦c≦2, 0≦d≦8, 0≦e≦4, 0≦f≦3, 0≦g≦8, 1≦o≦2, 1≦p≦5, 0≦h≦2, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 2:a(MIO).b(MII2O).c(MIIX).(4-a-b-c)(MIIIO).7(Al2O3).d(B2O3).e(Ga2O3).f(SiO2).g(GeO2).h(MIVxOy)  <Chemical Formula 2>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Au, and Ag; MIII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Mn; MIV is at least one selected from the group consisting of Bi, Sn, Sb, Sc, Y, La, In, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; X is at least one selected from the group consisting of F; Cl, Br, and I; and a, b, c, d, e, f, g, h, x, and y are respectively set in the ranges of: 0<a≦4, 0≦b≦2, 0≦c≦2, 0≦d≦1, 0≦e≦1, 0≦f≦1, 0≦g≦1, 0<h≦0.5, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 3:a(MIO).b(MIIO).cAl2O3.d(MIII2O3).e(MIVO2).f(MVxOy)  <Chemical Formula 3>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Mn; MIII is at least one selected from the group consisting of B, Ga, and In; MIV is at least one selected from the group consisting of Si, Ge, Ti, Zr, and Hf; MV is at least one selected from the group consisting of Bi, Sn, Sb, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; and a, b, c, d, e, f, x, and y are respectively set in the ranges of: 0<a≦1, 0≦b≦2, 0<c≦8, 0≦d≦1, 0≦e≦1, 0≦f≦2, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 4:a(MIO).b(MIIO).c(MIIIX).d(MIII2O).e(MIV2O3).f(MVoOp).g(SiO2).h(MVIxOy)  <Chemical Formula 4>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Mn; MIII is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Au, and Ag; MIV is at least one selected from the group consisting of Al, Ga, In, and B; MV is at least one selected from the group consisting of Ge, V, Nb, Ta, W, Mo, Ti, Zr, Hf; and P; MVI is at least one selected from the group consisting of Bi, Sn, Sb, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; X is at least one selected from the group consisting of F, Cl, Br, and I; and a, b, c, d, e, f, g, h, o, p, x, and y are respectively set in the ranges of: 0<a≦2, 0<b≦8, 0≦c≦4, 0≦d≦2, 0≦e≦2, 0≦f≦2, 0≦g≦10, 0≦h≦5, 1≦o≦2, 1≦p≦5, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 5:a(MIO).b(MII2O).c(MIIX).d(Sb2O5).e(MIIIO).f(MIVxOy)  <Chemical Formula 5>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Au, and Ag; MIII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Mn; MIV is at least one selected from the group consisting of Bi, Sn, Sc, Y. La, Pr, Sm, Eu, Tb, Dy, and Gd; X is at least one selected from the group consisting of F, Cl, Br, and I; and a, b, c, d, e, f, x, and y are respectively set in the ranges of: 0<a≦2, 0≦b≦2, 0≦c≦4, 0<d≦8, 0≦e≦8, 0≦f≦2, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 6:a(MIO).b(MII2O).c(MIIX).dGeO2.e(MIIIO).f(MIV2O3).g(MVoOp).h(MVIxOy)  <Chemical Formula 6>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Au, and Ag; MIII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, and Cd; MIV is at least one selected from the group consisting of Sc, Y, B, Al, Ga, In, and La; MV is at least one selected from the group consisting of Si, Ti, Zr, Mn, V, Nb, Ta, W, and Mo; MVI is at least one selected from the group consisting of Bi, Sn, Pr, Sm, Eu, Gd, and Dy; X is at least one selected from the group consisting of F, Cl, Br, and I; and a, b, c, d, e, f, g, h, o, p, x, and y are respectively set in the ranges of: 0<a≦2, 0≦b≦2, 0≦c≦10, 0<d≦10, 0≦e≦14, 0≦f≦14, 0≦g≦10, 0≦h≦2, 1≦o≦2, 1≦p≦5, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a phosphor represented by the following Chemical Formula 7:a(MIO).b(MII2O).c(MIIX).dP2O5.e(MIIIO).f(MIV2O3).g(MVO2).h(MVIxOy)  <Chemical Formula 7>
(where MI is at least one selected from the group consisting of Pb and Cu; MII is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Au, and Ag; MIII is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, and Mn; MIV is at least one selected from the group consisting of Sc, Y, B, Al, La, Ga, and In; MV is at least one selected from the group consisting of Si, Ge, Ti, Zr, Hf, V, Nb, Ta, W, and Mo; MVI is at least one selected from the group consisting of Bi, Sn, Pr, Sm, Eu, Gd, Dy, Ce, and Tb; X is at least one selected from the group consisting of F, Cl, Br, and I; and a, b, c, d, e, f, g, h, x, and y are respectively set in the ranges of: 0<a≦2, 0≦b≦12, 0≦c≦16, 0<d≦3, 0≦e≦5, 0≦f≦3, 0≦g≦2, 0≦h≦2, 1≦x≦2, and 1≦y≦5)
The first or second light emitting part may comprise a single or a plurality of phosphors.
Meanwhile, the fist and second LED chips may emit blue or UV light.
The light emitting device may further include a controller to control voltage applied to at least one of the first, second, and third light emitting parts. The controller may adjust the externally input voltage according to time, and particularly, may adjust the externally input voltage on a 24-hour cycle.
The first to third light emitting parts may be formed in a single package. The package may include a substrate upon which the first to third light emitting parts are mounted, and the phosphors of the first and second light emitting parts may be disposed above the first and second LED chips. Further, the package may further include a heat sink to dissipate heat generated from the LED chips, and the first to third LED chips may be disposed above the heat sink and the phosphors of the first and second light emitting parts may be disposed above the first and second LED chips.
The second light emitting part may be disposed nearer a center of the package than the first and third light emitting parts.
In the above description, although the first and second light emitting parts are divided based on a color temperature of 6000 K, the first and second light emitting parts may be divided based on a different color temperature. In accordance with another aspect of the present invention, a light emitting device includes a first light emitting part including a first LED chip and a first phosphor and emitting white light having a higher color temperature, a second light emitting part including a second LED chip and a second phosphor and emitting white light having a lower color temperature, and a third light emitting part including a third LED chip emitting light in the visible range of 580 nm or more. The second and third light emitting parts are operable independently of the first light emitting part, and realize a warm white color having a color temperature of 3000 K or less with the white light emitted from the second light emitting part and the light emitted from the third light emitting part. Accordingly, the light emitting device can realize white light having a variety of color temperatures. Meanwhile, a reference color temperature classifying the first and second light emitting parts may be in the range of 4000˜6000 K.